It may be of importance to locate or track a user when the user is inside a building. However, a well-known outdoor positioning system employing a global positioning system (GPS) may not work inside a building due to lack of reliable reception of satellite coverage. Therefore, a positioning technique utilizing Earth's magnetic fields indoors has been developed as one possible option for indoor location discovery. This type of location discovery applies, for example, a magnetic field strength measured by a positioning device. The measured strength is compared to known magnetic field strengths in the building in order to locate the positioning device and, thus, the person associated with the positioning device. However, several problems are related to this type of location tracking, especially to generating an indoor magnetic field map usable for the indoor positioning based on Earth's magnetic fields.